They posted the major leagues’ best record at 59-36. They landed six players in the All-Star Game, most of any team.

Yet with all they accomplished, the truth is that absolutely nothing is guaranteed moving forward. They lead the American League West by just 1 ½ games over the Los Angeles Angels, who happen to boast the majors’ second-best record.

There appears precious little margin for error. With that in mind, here’s a look at five questions facing the A’s as the second half awaits:

1. Can they guard against a letdown?

One of manager Bob Melvin’s strengths is his ability to maintain his team’s focus. And surely his players know they can’t take anything for granted with the Angels stalking them closely.

Still, can things possibly go as swimmingly as they did in the first half, when the A’s won more games (59) before the All-Star break than any team since the 2006 Tigers?

One thing going in their favor: They posted an otherworldly run differential of plus-145 in the first half. That suggests there wasn’t a lot of luck involved, where narrow victories could have just as easily wound up in the loss column. Something else to consider: According to ESPN’s Buster Olney, the A’s have the easiest second-half schedule of the 17 teams still in realistic postseason contention. Just 29 of their remaining 67 games are against teams currently at .500 or better.

That’s what you call Anti-Bulletin Board Material, the kind of fact that no manager wants his players to hear about, lest they take their foot off the gas pedal.

2. Can Samardzija, Hammel make a difference?

The A’s saw a need to bolster their starting rotation. They did so by swinging a blockbuster trade with the Cubs to land right-handers Jeff Samardzija and Jason Hammel. Those two will start the first two games out of the All-Star break, and the A’s need them to make their presence felt in their new environment.

Samardzija is pitching in the American League for the first time. And let’s face it, spending his entire career with Chicago until now, it’s been a while since he’s performed under the glare of pennant-race pressure. The Cubs last finished with a winning record in 2009, his second big league season. But Samardzija and Hammel -- who pitched in the postseason with Colorado and Baltimore -- are both energized to join a team in the pennant race. A’s general manager Billy Beane said he believes Samardzija -- a former All-America receiver for Notre Dame -- has the right personality and competitiveness to fit in at the front end of the rotation.

It sounds like a cliché at this point to talk about the veteran leadoff man being the A’s catalyst. But it’s true. Oakland’s offense clicks along at its most efficient with Crisp healthy and getting on base with frequency. The switch hitter has started just 62 of the A’s first 95 games this season. That’s partly due to a variety of injuries and partly by design. With Craig Gentry in the mix this season, Melvin knows he’s got a quality backup in center and therefore is resting Crisp more.

But the A’s have a fight on their hands with the Angels -- and potentially the Mariners -- and having Crisp atop the lineup consistently over the final two-plus months would be a big lift.

4. Can Sean Doolittle continue to close the deal?

The hard-throwing lefty stepped into the ninth-inning role and stabilized the back end of the bullpen. The numbers were sparkling over the first half -- 14 saves, 63 strikeouts, 2 walks in 43 2/3 innings. Can he maintain his level of dominance over the second half? There’s a good chance he can if he continues to mix in an effective slider just to keep hitters from guessing on that mid-90s fastball that’s been so effective to this point. Doolittle has thrown the breaking pitch more often this season than the previous two, but his MO is still to rear back and blow the heater past opponents.

5. Should the A’s add another piece to the puzzle?

Beane struck early with his big move by acquiring Samardzija and Hammel. But he said he and his staff will continue to be active in trade discussions if they find the right deal. Everyone is speculating whether the A’s will try to upgrade at second base, and there are definitely some middle infielders available. Would the A’s be willing to part with any of their surplus pitching to land one? Do they have enough prospects left in their system to entice a team that’s out of contention?